Process for the reproduction of graining



Sept. 5, 1939. F. L. LEE

PROCESS FOR THE REPRODUCTIONv OF GRAINING '.Filed May 26, 1937 Fos/ 7/vs 770S/TIVE IVEGA 11v:

Pas/TI v5 POS/ T/ VE A/EGHTIVE m m m w Patented Sept. 5, 1939 UNITEDSTATES PATENT OFFICE PROCESS FOR THE REPRODUCTION OF GRAINING 4 Claims.

This invention relates to processes for reproducing natural surfaceeffects, pictorial effects, combination of designs and decorations, andparticularly wood grains.

Certain varieties of wood are characterized by relatively complex andstriking grain patterns, which it is especially desirable to reproduceon metal or other surfaces. Examples of these are English oak burl,Australian lacewood, quartered l0 oak, birds-eye maple, Sequoia redwood,burl walnut, and various hardwood crotches. Such grain patterns producea visual impression aggregating three distinct effects, namely, (first)an effect of grain lines and stipple, (second) a wave or ripple effect,involving light, medium and dark shading or tone variations, and (third)a characteristic color effect.

An object of this invention is to provide a method which permits moretone value to be transferred from the resulting printing matrix plate.

A further object is to provide a matrix printing plate having maincavities of approximately equal depth, that give a low loss transfer oftone value 2:5 to the final offset and allow proportionate tone valuesto remain under pressure required in transfer.

Another object of the invention is to produce a matrix printing plate bya process adapting it to secure, by a single transfer operation, boththe first and second aforementioned visual effects, and to combine them.in their true natural relation.

Another object is to provide a process for the 3 aforesaid purpose,which, when once performed, requires no repetition of early steps tosecure any desired number of identical matrix printing plates.

A further object is to reproduce on a matrix ii-l plate, by a singleetching operation, a pattern reproduction of the whole and completevisual appearance of the master pattern or sample to be reproduced, saidappearance including the impressions of grain line and stipple and theim- 45 pression. of the wave or ripple effect, and to establish exactregistration of these effects upon the matrix plate to conform to thespecimen.

A further object is to produce a matrix plate that will morecontinuously portray a full tone 5!) appearance of the image of a woodspecimen or other surface. It is found in processes including theetching of cavities below the plane of the metallic surface of thematrix plate, that (with the exception of those high light areas as dic-05 tated by the natural surface copied), the unaltered top surface whichremains between the cavities, deducts more or less from the continuityof the tone value of the specimen or master pattern in proportion totheir expanse.

When a master pattern, the face of which is made up of small spots isviewed, the eye fuses the light reflection as a sense of tint. The eyeis unable to readily distinguish these components but sees only theirintegrated effect. The size and number of these spots modifies the tint,the 0 smaller, more numerous and closer together they are, the strongerthe tint. It is therefore highly desirable in reproducing a full tonedimage, to break up this surface effect, merging these spots to a certainlimit, thereby effectively increasing 16 the continuous tone effect.

For example: In the photo engraving process gradation of tone is securedthrough the employment of a mechanical screen having equal lines andspaces, and placed as an obstruction between 20 the lens aperture andthe sensitized taking plate. This process was originally developed forimprinting on a light paper background and produces, to a degree, thefeeling of continuous tone by so-called typographic letter pressprinting and lithograph or off-set printing, but upon examination itwill be noticed that tone value is less continuous than it would seem tobe. If this photo engraving process is employed in making intaglioplates by reversing the negative, there is a very appreciable loss oftone value as compared with the full tone of the specimen, owing to thelarge expanse of top surface that remains between cavities.

And for example: In the photogravure process which was likewiseoriginally developed to imprint on the surface of light backgroundpaper, the tone positive is screened by permitting the light to strikethrough transparent line rulings on a sensitized carbon tissue. Theselines erase part of the image and in their aggregate, such obliterationvery materially subtracts from the active image. If this process be usedin producing intaglio plates, an appreciable loss will be seen in thefinal offset owing to the expanse of 25 top surface seen betweencavities, thus introducing a loss in the image.

In my process, an absolute continuous tone photographic negative or acontact diapositive therefrom, or a reverse negative, photographed in)from. an original specimen surface, is transformed into an image that isonly slightly minus in tone value from the absolute continuous tonevalue of the specimen. This process is capable of producing tone valuewith unusual definition of detall and with a truer feeling of gradationof tone, as well as more faithful interpretation of highlights whichcome out with clarity and pureness that gives striking contrast to thedarker tone values in the composition of the image. After thetransformation, the difference between the transformed image and theabsolute continuoustone image taken from the specimen, results from asubstantially unaltered top surface in. the final matrix plate, whichsurface is utilized as :a grid to keep the doctor blade on the surfaceplane of the plate. The structure of the upper face of the plate thusprovided, is very finely divided and is closely related to thesurrounding low-loss cavities, it being dictated by the specimen,eliminating the use of the usual mechanical grid of geometric designwhich grid always introduces considerable loss in any image in theformation of which the grid is used.

Thu upon transferring pigmented matter from the cavities of my matrixplate to the surface which receives the final offset, increased accuracyof the reproduction is evident because the continuity of the image ismade possible by placing the cavities in close relation and connectingthe cavities, one with another, (with the exception of thosehigh-lighted areas) so that there are lesser and smaller spaces to beobliterated when the pressure of final imprint merges the materiallifted from one cavity of the matrix plate into the material lifted froma neighboring cavity.

For the purpose of illustrating the several steps of my process, I haveprovided the accompanying drawing illustrating diagrammatically theseveral steps of my process.

If a wood specimen or master pattern I having prominent surface grainlines and stipple is to be simulated in appearance by the employment ofmy improved process, it is usually necessary to first suitably treat thenatural grain surface to be reproduced. Ordinarily this surface is thatof a veneer, which may be glued or otherwise suitably secured to ahardwood board, and then dressed down to present a smooth, fiat faceclearly showing the grain of the wood. Upon such face, adjacent toopposite margins thereof, are impressed indentations, which, arepreferably filled with suitable material to sharply distinguish themfrom their background. After waterproofing the bottom and edges of theblock and the veneer edges, the grained face of the specimen or masterpattern i is coated with shellac, and then waxed and polished.

The grained face of the master pattern is then photographed to obtain anordinary negative 2 (preferably on glass), conforming exactly in itsdimensions to the mastern pattern. Such. negative, accurately depictsthe grain as regards the size, shape, and relative locations of thevarious spots, lines, or other definite markings, but fails, due to wellknown limitations of photography, to represent all of the true relativetone values of the pattern. Such negative may be quite faithful ingeneral respects, but is not sufficient in itself to providea-mechanical vehicle which will necessarily characterize the dominantvalues and gradations that are seen in the master specimen or pattern.An increased value may be had to improve the final appearance, byeventually adding to the image a stronger interpretation of theprominent grain lines and stipple and other values, by retouching thenegative, and for use as *a guide in such retouchingit is preferred tonow make from the negative, a positive print 3 on paper suited toreceive and retain pencil or crayon markings for use only as amemorandum check.

All overtones of the wood specimen I are progressively noted andaccurately indicated with crayon on the print 3, securing exactrespondence of tone between the specimen and print in all areas, anyunduly dark areas of the print being identified for future reference bycolor or other handwork.

The positive print 3, as thus prepared, serves as a guide in retouchingthe negative 2 by laying the print face down, upon a glass plate 4having a strong light therebeneath with this negative superposed uponthe print 3 and with the graining reproductions in an exact registryestablished by the aforementioned positioning marks. The emulsion faceof the negative 2 is uppermost, and has cemented thereto a thin tissue4a of transparent paper, suited to receive and retain crayon markings.With the negative thus illuminated through the retouched print 3, it isreadily feasible to fill in with crayon on the tissue, all overtonesindicated on the print and to subdue or eliminate, any blemishesappearing as overtones on the print. Also at this time, certainpredominating grain lines and grain stipple are subdued, removed orstopped out, whereby the grain reproduction on the negative issubstantially limited to the ripple or Wave effect and any whorl effectsorother major variations of the master pattern. The retouched negative(formed of the negative 2 with the tissue 4a cemented thereto) isindicated at 2a.

The next step is to transform the continuous tone image of the retouchednegative 2a into pure line and irregular specks, having equal opacityand density, which produce in their aggregate, an image of practicallyno loss. (Either an original continuous tone negative or positive may betransformed. The transforming of a negative will now be dealt with. tologically follow previous steps.) This step will be referred to as thetransformer plate 5 which consists of a thick plate of glass, having afinely ground working face to which are initially applied severalalbuminous coats containing potassium silicate, and such initialcoating, when thoroughly dry, serves to cause a sensitizing coating tofirmly adhere thereto and is the basis for a finely reticulated surfacedue to its bichromated gelatin content, the importance of this effectappearing hereinafter.

Against the sensitized face of this thick glass transformer plate 5,there is now placed the retouched negative 2a, and light is transmittedthrough the latter to such face, and photochemical action takes place.The gradated and varied tones in the negative, prints or hardens thegelatin face as indicated at 5a in proportion to the densities of thevaried tones. Where light has reached the sensitized face of thetransformer plate 5, portions of the bichromated coating become more orless insoluble.

The plate is now washed to remove all traces of unaltered portions ofthe bichromated coating, and as washing continues, different parts ofthe coating absorb water according to the degree of light which reachedit through the negative. This gelatinous coating appears to swellforming minute bubbles or proturbances, and is then allowed tothoroughly dry and when dry the face is found to have broken up intominute reticulations that vary in water retaining ability.

This gelatinous coating is now subjected to immersion in water for ashort period, and then allowed to slowly evaporate. The coating is nowpartially dried and the effect of this treatment is that the gelatinousface has absorbed water throughout definite portions thereof asdetermined by the aforementioned exposure to light through the retouchednegative The next step lies in inking the surface of the transformerplate 5, asby a suitable inking roller, said roller having been chargedwith opaque, greasy ink, isthen firmly pressed against the surface thusprepared and the ink adheres only to those completely insoluble portionspreviously affected by light. The inked image thus produced, becomesaneffective transformation, of the continuous tone image on the retouchednegative 2a, toa positive image of uniformly dense and opaque black andapparently continuous tone as viewed by the average naked eye, but infact is interrupted by multitudinous minute, feathery open areas ofirregular'size and shape, due to the aforementioned reticulated surfaceof the gelatinous'coating. Ink appears to adhere in a dense manner tothe central part of the reticulations, some of which have cracked oropened, and is slightly less dense at the edges, all solubleportionscontain moisture, having refused to take the ink. This formationoccurs in the deeper tones of the image, but for the lighter tones andhigh light areas of the image which are composed of lighter, frailer,smaller and fewer reticulations to a given area, the ink appears toadhere in a dense manner only to the central portions of thereticulations and is very much less in evidence at thefeathery edges.Thus such a transformer plate provides a highly accurate representationof the ripple or wave motion effect of the grained surface of theoriginal Wood specimen to be reproduced, the form of its reticulationsbeing directly controlled by th specimen itself. This transformed plateis now allowed to dry off for several days.

There will now be described a method of accurately reproducing the grainline and grain stipple effect of the wood specimen or master patterntreated as above described, and indicated at la;

To the grained surface of the specimen la is applied a liquid(preferably hot) of a nature to be rapidly absorbed by the softersurface portions of the veneer, namely, those portions within the poresand other grain depressions of the surface, but the simple applicationof water will accomplish' the same result, taking a greater period oftime to swell up portions within the pores. A very effective solutionfor th s purpose includes caustic soda, wood alcohol, and paraffin. Thissolotion is continuously brushed back and forth on the grained surfaceuntil resultant swelling of the softer surface portions raises the sameabove the general surface level. These raised portions may now be wipedfree of the surface by a brush or the like, the wiping operation beingrepeated at intervals until the grain lines and stipple are sufficientlylowered beneath the surface level. Treatment of the specimen la is nowcompleted to produce specimen lb, by washing the grained surface withalcohol, removing the alcohol, thoroughly rinsing said surface withwater, and finally allowing the specimen to thoroughly dry.

The next step consists in applying to the grained surface of specimen lbby adhesion, a thin uniform coating of a fluid or semi-fluid materialsuch as will not readily penetrate the grain depressions. For thispurpose engravers black proving ink may be thinly and evenly applied byan inking roller or other suitable means to the entire surface of thespecimen, exclusive of its grain depressions, forming a negative patternof such depressions.

From the specimen lb thus inked, there is taken under suitable pressure,an imprint on thin oiltreated translucent tissue, the uninked areasthereof forming an. accurate, sharply defined negative pattern 9 of thegrain lines and grain stipple of the wood specimen lb. This pattern willbe referred to as the grain line and stipple tissue negative 9, and willbe added to the image.

It is now desirable to build up the density and choke up and partlyclose the feathery open areas of the transformer plate 5 and combine itwith the grain line and stipple tissue negative 9. The transformer plate5, containing the positive image of ripple and Wave effects, havingdried off, is now contacted to a sensitized glass plate It] in asuitable vacuum frame and by photochemical action is reversed to anegative image ll on said plate with a gentle light source of a fewseconds duration, which renders the less dense edges of thereticulations to benneficially choke up causing some of the particles toremain isolated and some to combine with their neighboring particles theglass plate it retains the full benefit of the previous retouchingoperation (performed on the original photographic negative 2a), it isdesirable to also retouch said image ll to further increase the accuracyof reproduction and eliminate all fiaws and correct blemishes. Saidnegative image ll lends itself readily to manual addition and correctionof tone values, as in its negative form it shows as opaque dense variedshapes of varying sizes, due to the linear composition of itscharacteristic formation on the positive ll] and the aforementionedgranular breaking up of the image. After retouching, the above negativeI l is contacted to another and final sensitized glass plate l2 in avacuum frame, which further builds up the continuousness of tone (theposition of register marks having been determined mechanically thereon)and by photochemical action the image is reversed to a positive imagel3; and at once, and by a succeeding and similar operation the grainline and stipple tissue negative 9 is also added by contacting (withpositioning marks located in perfect register,) to the final sensitizedglass plate l2. The foregoing operations produce a double or superposedpositive transparency (formed of the plate l2 with its positive imagel3, and the tissue 9) of vastly greater continuous tone which has thecomplete image in opaque black on a transparent field of the originalwood specimen with (first) the grain line and stipple efiect and(second) the ripple and wave effect combined. This final image thusgives all major and minor tone variations in close continuity, all inrelation precisely conforming to the original master wood pattern. Thisfinal positive transparency may also he rctouched to remove minuteblemishes or close open spots due to limitations of the felatinouscoating.

The next step is to transfer the complete positive image of grain lineand stipple and ripple and wave effects from this final transparency l2to a metal matrix-forming plate Id. The latter, which is preferablysheet copper, has its working face first suitably cleaned and dressed,and upon said face is then dried sensitized enamel solution or the platemay be sensitized by the dry enamel process, or the cold top process orthe bitumen process, all well known in this art.

The desired transfer is effected by exposing said sensitized coating onthe matrix plate 14 to light through the final transparency, in asuitable printing frame. After the matrix-forming plate [4 is washed todissolve soluble portions of the coating, the latter is hardened to aresistforming enamel. The metal exposed between interstices of suchenamel now forms an accurate positive pattern of the grain lines andstipple of the wood specimen. Etching of this pattern into thematrix-forming plate is preferably ac" complished electrolytically, butthe desired result may be approximated by exposure of the resistcoatedsurface to any suitable mordant.

After applying an acid-resisting lacquer or varnish to the back andedges of the matrix plate, such metallic surfaces of the face of thematrix as show through the negative enamel resist is thoroughly cleaned,preparatory to etching.

By immersion in a thoroughly hydrated iron chloride solution (or othersuitable mordant) the plate is now etched, as dictated by the enamelresist and when properly conducted, the etching process is productive ofsmooth surfaces and straight walled grain cavities suited to readilyreceive and release greasy or fatty pigment or other coloring matter.

The resist-forming enamel is now removed by heating the matrix plate,then brushing its face with a solution of potassium cyanide and finallyneutralizing the potassium cyanide by hydrochloric acid.

The matrix plate I4 is now completed, having been etched to carry two ofthe said three primary visual affects, namely, (first) that of the grainand stipple effect, and (second) that of ripples, waves and major andminor tone variations, all in a relation precisely conforming to theoriginal specimen or master pattern I and with the image thereofimbedded below the surface in the metal.

The formation of the incised image does not include a geometrical designand in its positive sense is a cavity formation of naturally co-joinedand relatively located depressions and is a composition of minute,irregular and jaggedly shaped depressions of varied form and of variouswidths in lateral dimensions, which depressions are con nected anddisconnected cavity combinations and linear troughs as well assegregated and isolated spots of varying area sizes, down to minuteareas.

Inasmuch as the matrix plate !4 of my process produces an image whichincludes a multiplicity of exceedingly fine divisions dictated by themaster pattern, the image-print to be finally offset from said plate,clearly and accurately interprets the tone values of the original woodspecimen, the exact appearance of which is to be reproduced, into termsof the breadth of a pigment rather than depth. Thus the final matrixplate has a variety of connected and disconnected cavities of differentsizes and irregular shapes,

-- that are relatively located as to number, size and closeness, causingbreadth of pigmented tone values (corresponding to the tone values ofthe original specimen) in proportion to the aggregate number of suchcavities, etc., to a given area and approximately equal depths of suchcavities.

Owing to the nature of etching with some mordants, an occasional veryminute exposed area will receive slightly less etching as compared withthat of a large exposed area during the same period of time, and as saidbroader areas etch deeper than areas of less breadth, and also etch to asubstantially uniform depth, the tone value expressed by the cavities ofequal depth asserts itself in the final print in terms of aggregationhaving physical breadth of pigment, thus giving greater tone expressionto prominent grain lines and stipple,the first primary visual effectbefore referred to,and this is especially so where grain prominence ismanifest in high light areas. This adds very appreciably to the realismof reproductions.

Use of this matrix plate in applying artificial grain reproductions tometal or other manufactured surfaces, conforms to well known practices,the plate being loaded with a suitable fatty or greasy pigment, thenwiped to remove substantially all pigment exterior to the etchedcavities, and a gelatin slab then rocked or rolled on the plate and thenover the surface to be treated, to transfer the pigment from the formerto the latter without material disturbance of the pattern.

Preliminaryto such use of the matrix plate, the surface to which theimage is to be transferred, receives a ground coating of oil pigment tosecure the (third) aforementioned primary visual effect, namely, that ofcharacteristic color.

As no two species of the same wood genus are alike, and vast visual aswell as structural differences appear in different kinds of wood andother surface effects to be reproduced, each subject presents a somewhatdifferent problem in the way in which it may be best simulated in usingmy general process of producing matrix plates. I may vary the steps insimulating a specimen having grain lines that are less prominent andwhere a Wave, ripple or line effect is most pronounced. I may treat thewood specimen as previously described, with the exception that the twoindentations or registry marks may be dispensed with, and except thatprevious to being shellacked, waxed and polished, the surface may befilled and rubbed with some dark material to give prominence to grainmarkings, thus dispensing with the preparations of the grain line andstipple tissue negative 9 previously described for making more prominentthe grain lines and stipple. The grained face may then be photographedto obtain an ordinary negative which will, as the case may dictate, besubjected to the customary retouching.

The next step is to transform the continuous tone image of the retouchednegative which image is the pattern of the whole, complete and generalvisual appearance of all grain line markings, by the method as outlinedfor the step referred to as the transformer plate 5. Subsequent stepsfollow those previously described including the etching of the matrixplate.

It is to be noted that in producing duplicates of any matrix plate, thefinal positive transpar ency may be again employed as described,elimihating any repetition of the prior portions of the process.

By the described process, the visual appearance of wood surfaces andother natural surfaces of intricate design and complex tone variations,may be reproduced with much closer simulation than has been heretoforeachieved.

The term grain line and stipple in the following claims, designates anypattern of relatively small markings presenting the appearance of spotsor lines, while any larger and more elaborate tone variations areincluded in the term Wave and ripple effect.

Having thus fully described my invention what I claim is:

1. In the production of matrix plates having the characteristic ofpresenting the grain line and stipple efiect together with the wavemotion and ripple effect of the surface grain of a wood specimen, andwherein the plate in offset service produces an image print accuratelyinterpreting the tone values of the specimen surface in terms of breadthof pigment rather than depth through the arrangement of the etchedcavities of the plate, the method of preparing the master plate fromwhich the matrix is produced, which method consists in first preparingthe specimen surface for photographing with the naturalness of thesurface maintained; photographing the specimen to produce a negativecontinuous-tone image of the surface to form the initial stage in thestage development of a positive plate; completing the positive plate bya stage development to cause the continuous tone characteristic to betransformed into an image of the ripple and wave effects with othermajor variations and with the image of reticulated characteristic; thentreating the specimen to cause the grain lines and stipple effects tobecome of intaglio characteristic to form a printing surface; producingfrom such surface an ink-imprinted translucent issue negative in whichthe grain lines and stipple remain sharply defined and uninked; and thenpreparing a master plate by superposing the positive plate andtranslucent tissue negative in registration relative to a sensitizedtransparent plate; and exposing the sensitized plate through thesuperposed positive plate and tissue negative to thereby provide acombined image upon the transparent plate with the tonal effects of thespecimen accurately portrayed and adapted to form the master plateemployed in producing the matrix.

2. A method as in claim 1 characterized in that the stage development ofthe positive plate includes the following steps: cementing a thin tissueof transparent paper to the emulsion side of the negative and thenretouching the negative by crayon or the like markings on the tissue tosubstantially limit the grain reproduction on the negative to suchripple, wave and whorl effects as may be present together with othermajor variations of the specimen master pattern to thereby form thesource of a plate adapted for contact exposure; then transforming theimage of the latter plate into an image of pure lines and irregularspecks having equal opacity and density by contacting the plate with atransparent plate carrying a surface coating of sensitized bichromatecolloid, and transmitting light through the image of such source plateto the face of the sensitized bichromate colloid coating; treating theimage-carried colloid surface with water to cause swelling of coatingcontent portions in accord with the light values controlled by thesource image with the maximum light values producing insolubility of thecoating; drying the transforming plate to thereby break the bubbles orprotuberances of the swellings to thereby transform the coating faceinto a minute reticulation characteristic in which the reticulationsvary in water retaining ability; immersing the transparent plate inwater, then slowly evaporating water content and partially drying theplate to provide a coating having absorbed water throughout definiteportions determined by the light values of the previous exposure; andthen inking the prepared plate with opaque greasy ink to therebytransform the surface into an image in which the continuous tone imagehas been transformed into a minutely reticulated image of the ripple andwave motion and other general variation effects presented by thespecimen surface and completing the positive plate.

3. In the production of matrix plates having the characteristic ofpresenting the grain line and stipple effect together with the wavemotion and ripple effect of the surface grain of a Wood specimen, andwherein the plate in offset service produces an image print accuratelyinterpreting the tone values of the specimen surface in terms of breadthof pigment rather than depth through the arrangement of the etchedcavities of the plate, the method of preparing the master plate fromwhich the matrix is produced, which method consists in first preparingthe specimen surface for photographing with the naturalness of thesurface maintained; photographing the specimen surface to produce anegative continuous tone image of the surface; subjecting the negativeto treatment to render the effective image dominant as to ripple andwave effects while preserving the continuous tone characteristic;producing an image of minutely reticulated characteristic from thetreated negative by contacting under exposure relation conditions thetreated negative with the sensitized bichromate colloid coating of atransforming plate and exposing the coating by light transmissionthrough the negative and thereafter developing the transforming plate tothereby produce an image of pure lines and irregular specks having equalopacity and density; applying an opaque, greasy ink to the developedtransformation plate to form a positive image; producing a negativetherefrom and subjecting it to retouching activities, and from itproducing a positive plate of the ripple and wave effects of thespecimen; additionally preparing a separate negative of the grain andstipple effects from the specimen; and thereafter preparing a masterpositive plate from which the matrix is produced by superposing inregistration the prepared positive plate and the separate negative underexposure relation conditions relative to a sensitized glass plate tothereby combine thereon the separate images to form the master plate.

4. A method as in claim 3 characterized in that the separate negative isproduced by the following steps: treating the specimen surface withliquid to swell the softer portions of the surface and raise them abovethe level of the harder portions of the surface to thereby graduallydevelop the grain lines and stipple effects of the specimen to become ofintaglio characteristic, then inking the non-depressed surface of thespecimen and applying thereto a thin oil-treated translucent tissue tothereby obtain an imprinted accurate sharply-defined negative pattern ofthe grain lines and grain stipple of the specimen surface and whichforms the said separate negative.

FRANK L. LEE.

